This invention relates to a process and apparatus for blowing or delivering coal and other carbonaceous dust to be combusted in a furnace of the type having several combustion points. More, particularly, this invention relates to a process and apparatus for delivering coal dust to an industrial furnace, particularly, a shaft furnace such as, for example, a blast or cupola furnace, wherein the coal dust is fed in dosed quantities to plural combustion points in separate air streams which are under a predetermined pressure. As mentioned, this invention also relates to an apparatus for delivering carbonaceous dust for combustion in an industrial furnace having plural combustion points. The apparatus comprises several conveyor lines or systems, each leading to a combustion point, for the coal carbon/carrier gas stream to be blown therein and which is under a predetermined pressure. Each conveyor line is connected at its end farthest removed from the combustion point to a pressure vessel which contains coal dust under a predetermined pressure and which is fluidized by air.
In recent years, particularly since the several "oil crises", a very considerable increase in fuel oil prices have occured. Consequently, the possibility of future shortages of available oil and further price increases have been resulting in efforts being made throughout the world to reduce the consumption of fuel oil. Accordingly, considerable efforts have a been made, particularly in the case of industrial firing installations i.e., industrial furnaces, to replace fuel oils by cheaper sources of carbon which are readily available outside the oil producing countries. The most readily available and cheapest source of such carbon is finely crushed coal in the form of coal dust.
Various apparatii for blowing coal dust into, for example, blast furnaces, have previously been developed in the United States and in the Peoples Republic of China. Apparatii of the type especially suitable for cupola furnaces have also been developed in the United States. Similarly, cylindrical rotary kilns for producing cement have been converted to coal firing processes and like efforts are being made at present to appropriately convert shaft furnaces in the same respect for the production of burnt lime.
Generally, in prior art processes and apparatii of the type discussed above, carbon in the form of coal dust has been delivered to plural combustion points in the furnace via volumetric or gravimetric quantities in a stream of carrier gas, i.e., conveying air. The quantity of carbon/carrier gas flowing into the furnace fluctuates as a function of the prevailing pressure in the furnace. It will be appreciated that the fluctuating internal pressure in the furnace may be caused by the different bulk densities of the material which have already been deposited in the furnace. However, it will also be appreciated that a fluctuation in the quantity of carbon/carrier gas fed to the furnace is undesirable from a stand point of efficiency and control.
While the fluctuating pressure and resulting uneven quantity of carbon being fed to the furnace as discussed above is an important disadvantage of the known processes and apparatii for delivering coal dust to an industrial furnace, another important disadvantage is that the quantity of coal being fed to each of the plural combustion points cannot be directly or indirectly determined as a function of the quantity of coal being delivered. In fact, in order to ascertain the quantity of coal dust fed to each combustion point, (and consequently to monitor uniform charging of carbon to the furnace at the individual combustion points), measured variables such as the pressure in the carbon/carrier gas stream must be used. However, it should be understood that such measured variables will not yield reliable information.
Furthermore, prior art coal dust blowing or delivering apparatus have been extremely expensive to manufacture and maintain. For example, in a well known blowing apparatus of the type hereinabove discussed, an individual cellular-wheel sluice having an appropriate control circuit must be assigned to each conveyor line leading to a combustion point in the furnace. Thus, for example, when 20 or 30 combustion points are present in a furnace, there is obviously a considerable outlay or expense in terms of investment and resulting costs for maintenance, repairs, etc.